This invention relates to a device for measuring the pulse width or/and the carrier frequency of a pulse modulated wave that very high-frequency carriers are intermittently sent out, such as, for example, an electric wave transmitted from a radar.
In general, there has not been developed a proper method for measuring the pulse width and the carrier frequency of a pulse modulated wave that its carrier signal is modulated by a pulse and that the carrier is intermittently outputted, such as an electric wave transmitted from a radar. A feasible method is to detect the pulse modulated wave with a detector and measure the pulse width of a rectangular wave obtained by the detection. However, in order that a rectangular wave having the pulse width corresponding to the duration of the pulse modulated wave may be derived at the output of the detector, a smoothing low-pass filter which has a time constant sufficiently larger than the cycle of the modulated wave is included in the detector and the pulse width of the smooth output signal from the low-pass filter is measured. Accordingly, the output from the low-pass filter has a dull waveform which rises and falls in accordance with the time constant of the low-pass filter. In the measurement of the pulse width of a waveform having dull rise and fall, a large error is inevitable, as is well-known in the art.
In the case of measuring the carrier frequency of the intermittently supplied pulse modulated wave with, for instance, a digital counter, a gate circuit for gating the signal to be measured can be controlled by the rise of the pulse modulated wave but it is difficult to detect the moment of termination of the pulse modulated wave. Therefore, the gating time of the gate circuit is set by presumption. On the other hand, since the frequency measuring method of the digital counter is to divide the number of input pulses by the gating time, the presumed gating time leads to lack of accuracy in measurement. In the case of a pulse modulated wave of a low frequency, the frequency of the modulated wave can be measured by suitable means such, for example, as an oscilloscope but it is regarded as very difficult to measure the pulse width and the carrier frequency of a pulse modulated wave of an extremely high carrier frequency such as a radar wave.
An object of this invention is to provide a pulse modulated wave measuring device which is capable of accurate measurement of the pulse width of a pulse modulated wave having an extremely high frequency.
Another object of this invention is to provide a pulse modulated wave measuring device which is capable of automatic measurement of the pulse width of a pulse modulated wave.
Another object of this invention is to provide a pulse modulated wave measuring device which is capable of automatic measurement of the carrier frequency of a pulse modulated wave having an extremely high frequency.
Still another object of this invention is to provide a pulse modulated wave measuring device which is capable of automatic measurement of the pulse width and the carrier frequency of a pulse modulated wave.